The present invention relates to the field of thermal protection materials for use in solid propellant thrusters. More precisely, the invention relates to tests and modeling means suitable for characterizing the thermal erosion behavior of thermal protection made using such materials under conditions that are representative of those to which they will be subjected in a full-sized thruster, i.e. at 1/1 scale.
The performance of thermal protection is evaluated as a function of its thermal erosion behavior in response to the gas generated by the combustion of the solid propellant. During combustion of the propellant in the thruster, under the effect of the high temperatures those portions of the thermal protection material that are exposed to the flow of combustion gas become degraded on the surface by forming coke, and the coke as formed in this way is subjected to erosion to a greater or lesser extent as a function of the degree of its exposure to the flow and of the speed of the flow. The thermal erosion behavior of a thermal protection material corresponds to evaluating its ability to withstand the temperatures and the aerodynamic forces encountered in the thruster.
One of the methods presently in use for characterizing the thermal erosion behavior of internal thermal protection for solid propellant thrusters consists in a modeling tool based on a semi-empirical relationship (erosion criterion) defined on the basis of experimental results obtained when testing 1/1 scale thrusters and for a specific type of material. Consequently, the modeling tool developed can be used only for characterizing the thermal erosion behavior of thermal protection made out of the material with which the 1/1 scale tests were performed.
Nevertheless, in order to improve the thermal erosion behavior of thermal protection internal to thrusters so as to reduce cost and/or weight, it is desirable to develop novel thermal protection making use of novel materials corresponding either to materials of a different kind, or to materials of the same kind but to which significant advances have been applied. Either way, the model available for thermal erosion calculation is not usable since it is based on an erosion criterion defined from a specific material. Consequently, for each new material, it is necessary to perform one or more tests at 1/1 scale in order to determine an erosion criterion and to have a calculation model that matches the characteristics of the material in question.
This need to perform one or more tests at 1/1 scale prevents performing prior studies at low cost that would make it possible to evaluate the improvements (in terms of performance and cost) that might be obtained by using a new material, and prevents dimensioning of thermal protection to be made with the new material in a thruster by calculation (modelization) at 1/1 scale.
Consequently, there exists a need to enable tests to be performed at lower cost, i.e. at a small scale, thus making it possible to avoid any need to perform test firings at 1/1 scale.
Existing reduced scale test means in use for characterizing the thermal erosion behavior of thermal protection materials make use of cylindrical extenders of small diameter (about 200 millimeters (mm)). However inspecting those tests show that the appearance of cokefied material and erosion levels found during such tests differ from those observed on thrusters at 1/1 scale. Although such tests make it possible to carry out comparative studies between two materials, they are not representative of behavior at 1/1 scale, and consequently they cannot be used for devising a calculation model that can be used for evaluating and dimensioning thermal protection for use in a thruster at 1/1 scale.